Cardiovascular disease is commonly accepted as being one of the most serious health risks facing our society today. Diseased and obstructed coronary arteries can restrict the flow of blood and cause tissue ischemia and necrosis. While the exact etiology of sclerotic cardiovascular disease is still in question, the treatment of narrowed coronary arteries is more defined. Surgical construction of coronary artery bypass grafts (CABG) is often the method of choice when there are several diseased segments in one or multiple arteries. Open heart surgery is, of course, very traumatic for patients. In many cases, less traumatic, alternative methods are available for treating cardiovascular disease percutaneously. These alternate treatment methods generally employ various types of percutaneous transluminal angioplasty (PTCA) balloons or excising devices (atherectomy) to remodel or debulk diseased vessel segments. A further alternative treatment method involves percutaneous, intraluminal installation of expandable, tubular stents or prostheses in sclerotic lesions.
A recurrent problem with the previous devices and PTCA procedures is their failure to maintain patency due to the growth of injured vascular tissue. This is known as “restenosis” and may be a result of the original injury to the vessel wall occurring during the angioplasty procedure. Pathologically restenosis represents a neointimal proliferative response characterized by smooth muscle cell hyperplasia that results in reblockage of the vessel lumen necessitating repeat PTCA procedures up to 35-50% of all cases. It has been generally accepted that a certain therapeutic agents or medicaments may be capable of selectively inhibiting the growth of these hyperproliferating smooth muscle cells and thereby reduce the rate of restenosis after the primary interventional procedure.
Heretofore, various devices have been disclosed which may be used to deliver a therapeutic agent or medicament to a blood vessel while undergoing angioplasty. Balloon angioplasty catheters have been used to place and deliver a various therapeutic agents or medicaments within human vessels. For example, in U.S. Pat. Nos. 5,112,305, 5,746,716, 5,681,281, 5,873,852, 5,713,863 and 6,102,904 disclose and claim a balloon catheter system with various injector plates mounted on the balloon for delivering a drug into an arterial segment.
Alternatively, a standard angioplasty balloon may be coated with a polymeric material which is then used to bond certain medicaments or therapeutic agents. These agents are then delivered to the desired therapeutic site by inflation of the balloon and diffusion of the medicament or therapeutic agent into the vessel wall. Only limited quantities of therapeutic agents can be delivered because of “wash-out” of the drug into the circulation during balloon placement and due to the limited time the inflated balloon can be left in place due to ischemia caused by the balloon.
In addition, previously disclosed methods of delivering drug to a site of treatment are described which utilize iontophoretic or electrophoretic means as disclosed in U.S. Pat. No. 5,499,971. Using these iontophoretic or electroporetic means passive diffusion of the drug or medicament is enhanced by placing the medicament or therapeutic agent in close proximity to the site of treatment and then using electrically to augment delivery of the drug into the tissues or cells. These methods generally place the drug inside a balloon mounted distally on a catheter whereby the balloon is composed of a semiporous material through which the drug can diffuse.
Alternatively the electrodes themselves may be used as a method for iontophoretic or electroporetic drug delivery. One such method is disclosed in U.S. Pat. No. 6,219,577 which describes coating the surface of band-like electrodes with a polymer which bonds the drug and delivers it to the site of treatment. This method has the disadvantage of not have the capability to dilate the obstruction prior or concurrent to the delivery of a drug. Additionally the surface area of contact of the electrode bands with the vessel wall are limited to only the central portion of the arc shaped bands. This limits the contact surface area of the drug coated electrodes. This method also has the inherent disadvantage that since the site of therapy is intravascular, most of the drug will be washed off or dissolved off the electrodes into the circulating blood stream before it is advanced through the vascular system from its percutaneous entry and to the distal site of treatment. This again limits the amount of the drug delivered to the site and also potentially subjects the patient to harmful or toxic systemic exposure.
Additional devices have been disclosed which attempt to improve the depth of penetration into tissue by pressure driving a solution of the drug into the vessel wall through small orifices in the balloon material. There is, however, some evidence that high pressure “jetting” of a drug solution out of small pores close to the vessel lumen can in fact cause vessel wall injury. The development of double skinned, microporous (or weeping) balloons obviated this “jetting” effect to some extent, but diffusion of the drug into the vessel wall is still slow, and much of the drug can be lost through subsequent “washout effects”. This method leads to limited amounts of drugs or therapeutics agents delivered to the tissues or cells. Furthermore, in all of these methods the balloon must be expanded and thereby restricts blood flow to the distal arterial segments while the balloon is in the expanded configuration thus limiting the time the drug delivering balloon can be clinically utilized.
There are also several disadvantages using either a stent or balloon catheter to delivery a therapeutic agent or medicament to a vascular segment. Regarding the therapeutic agent eluting stents, once the stent is deployed, there is no means outside of invasive surgical excision, to remove the eluting stent from the vascular segment. Therefore, stents or implanted prostheses with therapeutic agent eluting properties must be precisely calibrated to deliver an exact quantity of the therapeutic agent or medicament to the vascular segment upon stent deployment. Balloon catheters employed to delivery a therapeutic agent or medicament to a vascular segment have limitations including potential balloon rupture and ischemia due to balloon inflation limiting distal blood flow to the artery. This leads to tissue ischemia and potential necrosis. Even “perfusion” type angioplasty balloons used to delivery a therapeutic agent or medicament to the affected artery provide far less than physiological blood flow during balloon inflation and dwell times are limited by ischemia and tissue necrosis.
Thus, it can be seen that there is a need for a new and improved device to selectively delivery a therapeutic agent or medicament to an arterial segment and which overcomes these disadvantages.
In general, it is an object of this present invention to provide a mechanical dilatation device and method which is capable of dilating an obstruction within a vascular segment while delivering, either passively or by an electrically active means, a therapeutic agent or medicament to the vessel segment.
Another object of the invention is to provide a percutaneous device and method of the above character which can be used for prolonged periods in exposing or delivering a therapeutic agent or medicament to a vascular segment while allowing continuous perfusion of blood into the distal to the treatment area.
Another object of the invention is to provide a device that can control the release or diffusion of a medicament or therapeutic agent to minimize potential systemic affects and maximize the diffusion or delivery of the medicament or therapeutic agent to the site of treatment.
Another object of the invention is to provide a device that is not susceptible to structural damage (balloon rupture) and subsequent release of therapeutic agents or drug materials into the vasculature.